Conventional steam power plants have a closed water-steam circuit, to which energy is supplied into the boiler feed water in the steam generator by burning a fossil fuel, such that it is transferred into the vaporous state of aggregation. This steam drives a generator via one or more steam turbines and is subsequently reliquefied in a condenser.
There have been attempts in the past to couple thermal energy into the water-steam circuit of a steam power plant that is fuelled with fossil fuels in order to thereby increase the electric power and/or reduce the fuel consumption.
For example, U.S. Pat. No. 4,069,674 discloses preheating a partial flow of the condensate in solar collectors and subsequently introduce it again into the pre-heating line. This method bypasses all preheaters. This means that the partial flow of the condensate is branched off upstream of the first preheater and, after passage through the solar collectors, the partial flow of the condensate, which has been preheated by solar energy, is coupled again into the main condensate flow downstream of the last preheater.
The partial flow that has been preheated by solar energy must have the same temperature as the main condensate flow preheated in the preheaters, which results in a large temperature difference of the partial condensate flow in the solar collectors. This large temperature difference can be achieved only on a few days during the year or within a few hours during the year such that the contribution of the solar collectors to preheating of the condensate is relatively small.
US 2008/0034757 A1 discloses a similar method, in which a heat exchanger is provided in series with the preheaters. The condensate is heated in this heat exchanger by thermal oil which has, in turn, been heated by solar collectors.
This method is disadvantageous in that the series arrangement of the heat exchanger causes additional pressure loss in the water-steam circuit even when no heat is coupled in via this heat exchanger, e.g. due to insufficient solar radiation. This system is moreover comparatively inflexible such that the solar collectors can provide an appreciable amount only in case of optimum solar radiation. The production costs are moreover relatively high, since all components must be designed to be high-pressure resistant.
WO97/14887 discloses a method for generating wet steam in a field of solar collectors. The wet steam can be directly fed into the separating bottle or the drum of the steam generator. This method is disadvantageous in that solar thermal energy is coupled-in only at a fixed temperature level and retrofitting requires interference with the steam generator.
In summary, one can state that these conventional steam power plants with solar thermal support have little flexibility with respect to temperatures at which solar energy can be coupled into the water-steam circuit. In consequence thereof, only a comparatively small part of solar energy contributes to generation of electric energy.
It is the underlying purpose of the present invention to provide a steam power plant and a method, which improve the contribution of solar radiation to the generation of electric power of a steam power plant having a fossil-fuel steam generator.